Catenary supported log periodic antenna



Sept. 6, 1966 R. JUSTICE CATENARY SUPPORTED LOG PERIODIC ANTENNA Filed Oct. 17, 1962 4 Sheets-Sheet 1 FIG-i PRIOR ART X,

PRIOR ART INVENTOR.

RAYMOND JUSTICE BY ATTORNEY R. JUSTICE 3,271,774

CATENARY SUPPORTED LOG PERIODIC ANTENNA Sept. 6, 1966 4 Sheets-Sheet 2 Filed 001;. 17, 1962 IN VENTOR. RAYMOND JUSTICE ATTORNEY Sept. 6, 1966 R. JUSTICE GATENARY SUPPORTED LOG PERIODIC ANTENNA Filed Oct. 17, 1962 4 Sheets-Sheet 3 INVENTOR. RAYMOND JUSTICE ATTORNEY p 6, 1966 R. JUSTICE 3,271,774

CATENARY SUPPORTED LOG PERIODIC ANTENNA Filed Oct. 17, 1962 4 Sheets-Sheet 4 II H H H II Ill) H H II H H H H H H H H H H II II IN VENTOR. RAYMOND JUSTICE z g A4441:

ATTORNEY United States Patent 3,271,774 CATENARY SUPPORTED LOG PERIODIC ANTENNA Raymond Justice, Lake Barcroft, Falls Church, Va.,

assignor to Granger Associates, Palo Alto, Calif., a corporation of California Filed Oct. 17, 1962, Ser. No. 231,200 3 Claims. (Cl. 343792.5)

This invention relates in general to high radio frequency antennas and, more particularly, to an improved and novel form of antenna of the logarithmically periodic type.

Log periodic dipole antenna arrays providing exceptionally broad frequency bandwidths have been proposed as, for example, by D. E. Isbell, IRE Transactions on Antennas and Propagation, May 1960, pages 260-267. Such antennas each include a pair of longerons serving as a twowire balanced feed line from each of which a plurality of radiating elements extend normal to the axis of the longeron. On each longeron, the linear radiating elements are coplanar, increase in length in logarithmic fashion from the feed end of the longeron, and extend alternately in opposite directions from the longeron. Radiating elements on the two longerons which are equal distance from the feed end are equal in length and extend in opposite directions normal to the longerons.

For high frequency communications systems, such antenna arrays are supported from two structural towers. The longest two radiating elements at one end of the feed line are suspended between the tops of the towers, the feed line comprising the two longerons extending from a point midway between the tops of the towers in an incline toward the ground where the other end or apex of the array is anchored. Catenaries also extend from the top of each of the towers down toward the apex where they are anchored, these catenaries serving to support the outer ends of the radiator elements which extend perpendicularly from each of the longerons and parallel with the ground.

The present invention provides a log periodic antenna array which obtains the broadband and other electrical characteristics of the aforementioned log periodic antennas, yet offers an unprecedented increase in system gain per incremental increase in system weight and volume. In particular, one form of the novel antenna of the present invention provides for greater ease of assembly and construction and greater portability, said antenna requiring the use of only one tower in place of the above-mentioned two towers.

It is, therefore, the object of the present invention to provide a novel and improved log periodic antenna of advanced design.

One feature of the present invention is the provision of a long periodic antenna wherein the radiating elements extending from the two-wire feed line are each positioned at an angle relative to the axis of the feed line which is different than 90 for improved electrical and mechanical characteristics.

Another feature of the present invention is the provision of a log periodic antenna of the above featured type wherein the angle 6,, that the plane in which the radiating element n and the longeron he makes with the vertical plane passing through the longitudinal axis of the longeron is greater or less than 90.

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Still another feature of the present invention is the provision of a log periodic antenna of the first above featured type wherein the angle (75,-, between the longitudinal axis of the longeron and the longitudinal axis of the radiating elementn extending from the longeron is greater or less than Another feature of the present invention is the provision of a log periodic antenna of the first above featured type for ground mounting wherein said feed line extends upwardly at an angle relative to the surface of the ground, and wherein said radiating elements extend outwardly from the feed line at an angle relative to the ground surface whereby said antenna, when constructed on the ground surface, may have the raised end thereof secured to the top of a single structural tower, the radiating elements extending down from the feed line and at an angle to the ground, the outer ends of the radiators being anchored to the ground.

These and other features and advantages of this invention will become apparent upon a perusal of the following specification taken in connection with the drawings wherein:

FIG. 1 is a schematic diagram of a log periodic planar transposed dipole antenna of known design,

FIG. 2 is a view of a log periodic non-planar transposed dipole antenna of known design,

FIG. 3 is a view of a structurally large antenna of the type shown in FIG. I mounted on the ground and supported by towers for use in high frequency communications systems,

FIG. 4 is a view looking down on and from the side of a ground-mounted, large antenna structure of the present invention,

FIG. 4A is a side view of the antenna of FIG. 4,

FIG. 4B is an enlarged view of a section of the antenna shown in FIG. 4,

FIG. 4C is a section view of the antenna structure of FIG. 4 taken along section line 4C-4C in FIG. 4B,

FIG. 5 is a plan view of another embodiment of the present log periodic antenna invention,

FIG. 5A is a side elevation view of a portion of the antenna of FIG. 5,

FIG. 6 is a side elevation view of still another embodiment of the present invention,

FIG. 7 is a view from the top and side of still another embodiment of the present antenna invention, and

FIG. 7A is a cross section of the antenna of FIG. 7 taken along section line 7A7A.

Referring now to FIG. 1, one known form of planar dipole log periodic antenna includes a feed line comprising two Wires or longerons 11 and 12 coupled together at the feed-in end by longerons 11 and 12 has a plurality of radiating elements 14 and 15, respectively, which are co-planar, vary in length in an increasing manner from the apex or feed-in end of the antenna, and extend alternately in opposite directions from their associated longerons. The linear elements 14 and 15 which are equal distances from the apex of the antenna, such as, for example, 14' and 15', are equal in length and extend in opposite directions. These longerons and radiating elements may be made of electrically conducting wires, tubing or the like.

This planar dipole antenna has design parameters oc,o', X and L which are governed by the frequency bandwidth and gain desired, where or is defined as the included 3 angle of the array, X is the distance measured along the longeron from the projected or true apex of the linear array to a radiating element It at some point on the longeron, L is the length of the radiating element 11, X is the distance from the true apex to the linear element immediately in front of n, L is the length of the radiating element immediately in front of n, is the ratio -tan E Typically, the length of the longest radiating element is one-fourth of the wavelength corresponding to the lowest operating frequency, and the length of the shortest radiating element is one-eighth of the wavelength corresponding to the highest operating frequency.

The gain of the antenna increases with increasing a and decreasing at; these are non-linear, monotonic functions over any discrete handwidth and are characteristic of log periodic structures. The function a is used as the design ratio of the antenna and most commonly falls within the range in values from 0.6 to 0.95. The radiation element positions derived from the ratio lie in geometric sequence.

Referring to FIG. 2 there is shown another antenna of known type termed a non-planar dipole log periodic antenna. This antenna includes one additional parameter over the antenna shown in FIG. 1, i.e. the angle 0 between the array comprising longeron 11 and associated radiating elements 14 and the array comprising longeron 12 and elements 15. In the antenna of FIG. 1, the angle a is zero.

The angle it in typical cases of non-planar type antennas varies about the value of 06 for any particular configuration. If 1/ is much less than a, it has been found that a sacrifice in gain occurs due to a broadened H- plane beamwidth, while, if 0 is much greater than oz, unsatisfactory front-to-back ratios have been found to occur. Therefore, a nominal design figure for \l/ in the case of a unidirectional log periodic array has been found to be 0.8ot ip 12a. The characteristic impedance of the array is a non-linear function of 1/ and thereby applies a normal design limit to 11/ and a of angles not to exceed 120. However, this factor applies only to the design of linearly polarized unidirectional antennas. In the case of a bidirectional antenna, the angle ,0 may be raised in value to 180, although in either instance the angle at should remain under 120 for optimum performance.

A form of non-planar log periodic antenna is described and claimed in U.S. patent continuation application Serial No. 319,828 filed by G. J. Van Osdol, Jr. on October 29, 1963 and assigned to the assignee of the present application.

In the antenna structures of the present invention, one or both of two additional variable parameters are utilized. One of these variables is the angle between the longitudinal axis of the longeron and the longitudinal axis of the radiating element It extending from the longeron which in the above-described antennas of FIGS. 1 and 2 is fixed at 90, or 1r/2. The other variable is the angle 0,, that the plane in which the radiating element It and longeron lies makes with the vertical plane passing through the longitudinal axis of the longeron, which in the case of the two previously mentioned antennas is 90 or 1r/2. These angles are shown in FIG. 2 and will also be illustrated in subsequent figures.

Referring now to FIG. 3, there is shown a known practical embodiment of the antenna structure of FIG. 1, useful in the application of high frequency communication systems, the antenna being very large and mounted on a ground surface. This form of conventional planar dipole requires two towers, 16, 17, between which the two longest radiating elements are stretched and secured, the two wire feed line 11, 12 extending down to the ground from between the tops of the two towers and being supported by a catenary. Two additional catenaries are necessary from the two towers to the ground to serve to support the outer ends of the radiating elements 14, 15 which extend parallel to the ground.

Several particular instances of the form that the new antenna may assume and typical applications of each form are described below.

One form of antenna has the parameters 0:0, 0 =+8, =90 and is shown in FIG. 4. In essence, the development from the standard transposed dipole of FIGS. 1 and 3 consists of rotating all of the radiating elements 14 and 15 through the same angle 6, the elements on opposite sides of the longeron rotating in opposite directions about the longitudinal axis of the feed line, rotation taking place in the plane of the radiating element and normal to the feed line axis. Because rotation on opposite sides of the feed line are in opposite directions, the angles 0 are referred to as 0,,(R) or 6,, on the right hand side looking along the feed line from the apex and 0 (L) or 6,, on the left hand side.

When used as an antenna in free space, this configuration performs in a manner quite similar to the planar transposed dipole of FIG. 1, at least for values of 6 up to 1r/6. The real significance of this antenna becomes evident when its structure is compared with the antenna of FIG. 3. The antenna of FIGS. 44C is easily supported from a single tower 18, the two -wire feed line 11, 12 extending between and being anchored to the top of the tower 18 and the ground. A single catenary 19 is required to support the feed line. The radiating elements 14, 15 are then slanted toward the ground, the outer ends of the elements being anchored as by guy Wires 21 to the ground. This distinguishes from the more complicated and expensive two-tower mounting arrangement necessary for the antenna design of FIG. 3.

Performance of this antenna is as follows: The polarization is horizontal and the bandwidth is h to f where f is the frequency at which the longest radiator is a half wavelength or slightly greater, and f is the frequency at which the shortest element is slightly less a half-wavelength. Power handling is essentially limited only by the design of the two-wire feed line. As to radiation patterns, the azimuth is approximately 60 and the elevation has a maximum near sin 1/ 4/2/1 where h is the phase center height above ground at A Beamwidth depends on 11/1 typically 50 for a beam maximum near 50 and 30 for a maximum near 25. This impedance is a function of feed line impedance similar to that for a planar transposed dipole.

An antenna of the type shown in FIG. 4 has been constructed to operate in the frequency band of 4 to 3 0 me. with log periodic performance. It employed a single transportable tower 70 feet in height. The angle 0,, of this particular antenna was 90+35, or

The elevation plane pattern is controlled by variations in height of the phase center above ground corresponding with changes in frequency. At the lowest frequency the phase center was 0.28 1 above ground, giving a 60 take-01f angle of radiation of the beam with respect to ground. At 30 me., the phase center was 0.5 t above ground, giving a 30 take-off angle.

VSWR was 2:1 or lower over most of the band, al-

' though under certain conditions it reached 3:1 at the lowest frequencynecessary to conserve tower height.

Two types of towers may be utilized, a telescoping and a tilt-up tower. The telescoping tower is highly mobile, compact and lightweight, consisting of a base section, folding pad and telescoping sections erectable in 30 minutes. A 70-foot telescoping tower employs five sets of guys, a 50-foot telescoping tower only three. Both sizes are conveniently cranked up by a hand winch which can hoist a ZOO-pound antenna as well as the tower sections.

The tilt-up tower is made up of quickly-connectable, durable aluminum sections weighing under 2 /2 pounds per foot. Coiled guys are preassembled to proper tower sections.

The feed line and radiator assembly may be completely preassembled and packed in a coil. The feed line contains a calibrated spring-tensioning device for quick, easy tensioning of the supporting element. Ends of the radiators, supported by dielectric rope, may be equipped with snap hooks and a means for rapid length and tension adjustments. Radiator stay anchor points may be easily located with a calibrated line.

In this and all of the special forms described below, the parameters on and may assume the values that have meaning for the planar transposed dipole, i.e., for example, O 0L 1r, 0 a 1.

Referring to FIG. 5, there is shown an antenna structure made in accordance with the present invention for radiating in a 360 pattern, said structure employing a variation in both the 5,, and 0,, parameters. This antenna utilizes a single central support tower 22 which supports the upper ends of four sets of two wire feed lines 11, 12, the opposite ends of the two wire feed lines being anchored to the ground. In this antenna, the radiating elements are all rotated downwardly toward the ground, as in FIG. 4, whereby 0,,(R) and 0,,(L) =1r/2-l-6 and at the same time each of the radiating elements is rotated toward the apex end of the array such that the angle ,,(R) and ,,(L)=1r/2+6'. It is noted that in FIG. 4 the angle was 1r/ 2 or 90. Rotating the elements to =1r/2+5 insures that the radiating elements nearest to the tower 22 in the different arrays do not overlap with the elements from the adjacent arrays, therefore, eliminating interference therewith.

There is shown in FIG. 6 an antenna structure in which the array is located in a plane perpendicular to the ground surface, the long-radiating element end of the array being secured to the tower 23 and the apex being anchored to the ground. In this antenna, the lower or right-hand radiating elements are rotated to an angle ,,(R)=1r/2+6 while the upper radiating elements are rotated to the angle (L)=1r/2-5, i.e. the upper and lower radiating elements remain in axial alignment but are not normal to the two wire feed line 24. Relative to the plane normal to the plane of the array, which latter plane in this instance is vertical to the ground, the angles 0,,(R) and 0,,(L) are 1r/2, or 90".

Referring to FIGS. 7 and 7A there is shown another form of log periodic antenna including longerons 27 and 28 with associated radiating elements 29. The parameters for this antenna are =0, (L) and ,,(R)=1r/ 2, 0,,(R)=n6, 6 ,(L)=n5, and 8:1r/2N, where N is the total number of pairs of radiating elements in the antenna. In the antenna shown, N 6.

If this antenna is oriented so that the longest radiator is in the horizontal plane, then it follows that the polarization of the radiation from the antenna rotates from horizontal at the lowest frequency to vertical at the highest frequency for which the antenna is designed.

An important application for an antenna in this form is to high frequency communication circuits where the circuit range is variable, such as in air-ground and shipshore communications. In such systems it is well known that higher frequencies are preferable for the longer circuits. This in turn leads to the requirement that the elevation power pattern have its maximum at low angles for high frequencies and intermediate to high at the lower frequencies. When the antenna described here is imaged over the earth with the low frequency element horizontal, the elevation plane power patterns closely approximate the optimum variation with frequency.

Refinements to the form factors described immediately above are easily obtained. Specific examples include =n1r/2, the other parameters remaining as above. This leads to an antenna that is essentially circularly polarized.

If the further modification is made of combining two planar transposed dipoles with their values of 0,, differing by 1r/2, the resultant configuration is again a circularly polarized antenna provided the elements of the two arrays differ in phase by in the log periodic manner. If their phases are equal, the result is a linearly polarized antenna.

Another antenna structure which embodies the present invention utilizes the parameters 0, 6,,(R) and 0,,(L) :1r/2+6 and (R) and (L)=vr/2. This antenna is similar to the one shown in FIG. 4 except the two longerons 11 and 12 are separated by an angle greater than 0. The H-plane gain and the antenna nominal impedance are increased over the antenna of FIG. 4. For the single tower application to high frequency communication antennas described in FIG. 4, this form has the advantage that lower elevation angles can be obtained without introducing the beam breakup that characterizes the patterns of both planar transposed dipoles and the antenna described in FIG. 4 when the tower height (phase center height) is raised to values much above M2 at the lowest design frequency.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A log periodic antenna structure comprising, two logarithmically periodic arrays having a common apex substantially at ground level, each of said arrays comprising an electrically conducting feed wire inclined upwardly and away from said apex, a single tower supporting the outer ends of said feed wires, the two feed wires of said arrays lying in a common vertical plane, mutually spaced, electrically conducting, linear radiating elements extending alternately to one side and then to the other side from each of said feed wires, said linear radiating elements of each of said arrays increasing progressively in length from the apex of the array going towards the supporting tower substantially in accordance with the relationship where L and L -l-l are the lengths of the nth element and the element in front of the nth element respectively and X, and X +1 are the distances of the same two radiating elements from the apex of the arrays, and 0' is less than 1, the elements extending from the feed wires in such directions that angle 0,, is different from 90 where 0,, is the angle between the nth element and the vertical plane containing both said feed wires and to either side of which said radiating elements extend, said radiating elements inclining downwardly to either side of the feed wires and insulating means connecting their outer ends to the ground.

2. An antenna structure according to claim 1 wherein said radiating elements are additionally inclined with respect to the feed wires towards the apex of the arrays.

3. An antenna structure comprising a plurality of antenna structures according to claim 2 having their feed wires aligned in different azimuthal directions supported from said single tower.

References Cited by the Examiner UNITED STATES PATENTS 2,977,597 3/196-1 Du Hamel et al. 343-792.5 3,108,280 10/1963 Mayes et al. 343792.5 3,110,030 11/1963 Cole 343-7925 3,134,979 5/1964 Bell 343792.5

(Other references on following page) 7 FOREIGN PATENTS 884,880 12/1963 Great Britain.

OTHER REFERENCES Jasik: Antenna Engineering Handbook, First ed., 5 McGr-aw-Hill C0rp., recieved P.O. Library October 9, 1961, pp. 18/10-18/31 relied on.

Du Hamel et al.: (I)-Log Antenna Design, IRE

8 National Convention Record, Part I, March 1958, pp. 139-151 relied on.

Milner: Log Periodic AntennasQST for November 1959, pp. 11-14 relied on.

HERMAN KARL SAALBACH, Primary Examiner.

E. LIEBERMAN, W. K. TAYLOR, Examiners. 

1. A LOG PERIODIC ANTENNA STRUCTURE COMPRISING, TWO LOGARITHMICALLY PERIODIC ARRAYS HAVING A COMMON APEXSUBSTANTIALLY AT GROUND LEVEL, EACH OF SAID ARRAYS COMPRISING AN ELECTRICALLY CONDUCTING FEED WIRE INCLINED UPWARDLY AND AWAY FROM SAID APEX, A SINGLE TOWER SUPPORTEDING THE OUTER ENDS OF SAID FEED WIRES, THE TWO FEED WIRES OF SAID ARRAYS LYING IN A COMMON VERTICAL, MUTUALLY SPACED, ELECTRICALLY CONDUCTING LINEAR RADIATING ELEMENTS EXTENDING ALTERNATELY TO ONE SIDE AND THEN TO THE OTHER SIDE FROM EACH OF SAID FEED WIRES, SAID LINEAR RADIATING ELEMENTS OF EACH OF SAID ARRAYS INCREASING PROGRESSIVELY IN LENGTH FROM THE APEX OF THE ARRAY GOING TOWARDS THE SUPPORTING TOWER SUBSTANTIALLY IN ACCORDANCE WITH THE RELATIONSHIP 